1. Field of the Invention
This invention relates to brakes, and in particular to an improved brake plate, as well as a method and apparatus for manufacturing the plate.
2. Summary of the Invention
The number of motor vehicles has increased greatly in recent years. There is an interest in methods of reducing the cost of manufacturing brakes and replacement parts on the part of both motor vehicle manufacturers and suppliers of parts for brakes. This increased use has also led to a significant increase in the after-market for brake replacement and repair. Brakes are also in increasing demand for motor vehicles such as airplanes, trains, bicycles, all terrain vehicles and motorcycles.
Brakes, as currently manufactured, combine two main parts, namely a plate (often called a backing plate) and a friction pad. The plate is mounted in a brake assembly, and may be formed by making a plate with a variety of bosses, holes, or other features for receiving and retaining the friction pad. The need to use high speed low cost manufacturing methods often results in irregularities in the plate which may lead to difficulties in attaching and/or retaining the friction pad on the plate during braking, when the friction pad is in contact with the rapidly turning brake rotor, or even during the pre-installation handling of the brake pad assembly.
There are a variety of known ways of attaching a friction pad to a plate. One such way is to attach the friction pad to the backing plates using rivets. One disadvantage of the riveting process is that it creates a rigid bond between the plate and the friction pad, which can, as result of a sudden impact, lead to breaking of the friction pad. Furthermore, this process often requires one or more additional manufacturing steps with a consequent increase in cost. In addition, when the friction pad is worn down over time, the rivets become exposed and rub against the brake rotor, causing scoring on the rotor which is costly to repair.
Another, more recently developed method of mounting the friction pad on the plate is to use a pressurized molding process to mold the friction pad directly onto the plate. In this process, the friction pad may be prepared by blending the components of the friction pad into a pre-form or cake. A conventional pressurized molding system is used to mold the friction pad pre-form onto the plate. A layer of cement or glue if often applied to the contact surface of the plate to improve the adhesion between the plate and the friction pad.
As pressure is applied to the mold assembly, the pre-form becomes heated and begins to flow, filling the mold and covering the appropriate surface of the plate. In this process, the pre-form material is intended to flow into and around the various features to improve the bond between the plate and the friction pad.
The plate is subjected to a number of forces, such as the jarring of the moving vehicle, as well as vibration caused by the rotor and noise. The problem with the prior art processes and plates is that features, such as holes and bosses, stamped into the plate often provided insufficient shear and/or tensile strength in the bond between the friction pad and plate. When additional features are stamped into the plate to increase bond strength, additional manufacturing steps are required, adding to the cost.
The most common prior art features stamped into plates are circular holes. These holes often provide unsatisfactory results because, during the molding process, the pre-form cake does not completely fill all of the holes, which in turn, leads to deficient bonding between the plate and the pre-form. The incomplete hole fills are clearly visible, and often raise quality concerns when inspected by buyers. The incomplete hole fills also have an aesthetically displeasing appearance, which can also make them less attractive to customers. Accordingly, it has become common practice in prior art plates to fill the incomplete hole fills with putty and to paint over them, to both hide the unsatisfactory molding results and to improve appearance. These additional manufacturing steps have the added disadvantage of increasing the cost of manufacturing the disc brake.
Furthermore, the holes stamped by prior art processes reduce structural strength of the plate, and make it more vulnerable to the various forces acting on it. These forces may distort the shape of the plate, leading to uneven wear on the friction pad, or can lead to structural failure of the plate.
Another problem with brake plates is caused by the heat generated by friction. The expansion and contraction values of the plate are different from those of the friction material. Braking generates heat so the plate and material are exposed to frequent heating and cooling. Since the expansion and contraction values differ, there may be a separation between the plate and the material, particularly where the plate is flat or has large flat areas. Rust can then form between the plate, which leads to noise and brake failure.
Accordingly, there is a need for a brake plate and a method of manufacturing same which can provide improved bonding with the friction pad without increasing the cost of producing the plate.